Integrated circuits are known to be used in a wide variety of electronic devices. For example, personal computers, cellular telephones, compact disk players, etc., all include integrated circuits. Such integrated circuits are comprised of a plurality of functional circuit blocks that perform desired functions. Transistors, resistors and capacitors generally comprise the circuitry found in each circuit block.
Frequently, different functional circuit blocks of an integrated circuit operate at different supply voltage levels that are provided from different power supplies. During power up of such an integrated circuit, the sequence in which voltages from the different power supplies rise to the respective supply voltage levels is important for proper operation of the integrated circuit and other components such as buses that couple to the integrated circuit.
A disc drive of the type used to interface with a host computer to store and retrieve user data includes integrated circuits that provide a controller for communicating between the host computer and the head-disc assembly of the disc drive. These integrated circuits of the controller are comprised of circuit blocks that operate at different supply voltage levels. For example, one integrated circuit of the controller includes an outer circuit block that operates at a first voltage level and an inner circuit block that operates at a second voltage level. This integrated circuit directly couples to the data exchange bus connected to the host computer. A switching regulator, which is coupled to a main power supply line, provides a first supply voltage at the first voltage to the outer circuit block. A linear regulator receives the first supply voltage from the switching regulator and provides a second supply voltage at the second voltage level to the inner circuit block. The second voltage level is lower than the first voltage level. This regulation technique, in which a lower voltage is regulated from a higher voltage, is simple, cheap and relatively noise-free. However, during power up of the disc drive, the first supply voltage rises before the second supply voltage can be regulated. This delay in providing the second supply voltage at the second voltage level during power up can result in intermittent electrical spikes or glitches and parity errors in the live data exchange bus that is coupled to the integrated circuit.
Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.